The objective of the proposed research is to elucidate the role of phosphorylation and methylation in regulatory events which take place during virus-host interactions, when changes in the pattern of both host and viral gene transcription occur. This problem will be approached by identifying and characterizing modified viral proteins and examining their role in regulating events in viral replication, including initiation of viral mRNA synthesis, processing of viral proteins, and inhibition of host macromolecular synthesis. Reovirus, a ds RNA virus, and vaccinia virus, a ds DNA virus, will be used to analyze various aspects of the problem. Both viruses possess virion-associated kinases and methylases. Reovirus will be used to investigate the presumptive regulatory role of phosphorylation because it possesses a specific kinase and no contaminating host gamma-ATP-dependent kinase activity is detectable in the virion. Experiments have been devised to determine whether phosphorylation is required for activation of the virion associated transcriptase by examining the kinetics of phosphorylation, the functional relationship of transcriptase and kinase and the termini of nascent mRNA for phosphoryl and methyl groups transferred from modified viral proteins. Vaccinia virus exhibits variable degrees of host inhibition in different tissue culture lines so that correlations may be made between methylase-induced modifications and cytotoxicity. Extracts of vaccinia infected cells will be examined for new methylase activities capable of altering the function of components of the host translation system.